The invention concerns a ventilation device with a breathing gas source, a control unit, and a connecting device for connecting the device to a ventilation mask, where the control unit is connected to at least one sensor for detecting a test parameter.
In addition, the invention concerns a method for controlling a ventilator, in which a breathing gas source is controlled by a control unit as a function of at least one test parameter.
A device of this type and the method for controlling the ventilator can be used, for example, in connection with so-called bi-level ventilation. The ventilator produces an inspiratory pressure and an expiratory pressure. Basically, it is necessary to distinguish among controlled ventilation, assisted ventilation, and mixed forms of ventilation.
In controlled ventilation, the respiratory parameters during inspiration are completely determined by the ventilator. There are basically two forms of controlled ventilation, namely, volume-controlled and pressure-controlled ventilation. In volume-controlled ventilation, a well-defined tidal volume is delivered breath by breath; the pressure can vary between the respiratory strokes as a function of resistance. The basis for the switch to the expiratory phase is the attainment of a predetermined target volume or inspiration time. In pressure-controlled ventilation, the therapeutic pressure is held constant. The resulting volume can vary as a function of mechanical respiratory parameters. The switch to the expiratory phase is controlled as a function of time.
In volume-controlled ventilation, the administration of a sufficient, well-defined gas volume per respiratory stroke is the main consideration. Pressure-controlled ventilation has the advantage that when the parameters are suitably adjusted, there are no impermissible pressure peaks to damage lung tissue. Of course, the administered tidal volume is strongly dependent on the cooperation of the patient with respiration and on the mechanical respiratory variables of resistance and lung compliance. On the other hand, volume-controlled ventilation basically makes sense primarily in the case of invasive ventilation, since leakage occurs during mask ventilation, and such leakage makes it impossible to measure the actual control parameter accurately, even when the leakage that occurs is included in the calculations.
In pressure and volume-controlled ventilation, the advantages of volume-controlled ventilation are combined with those of pressure-controlled ventilation. The administered ventilation volume depends on the mechanical properties of the lung and on the ventilation pressure. If the volume falls below a preset value, the inspiratory pressure is increased in small increments during the following respiratory strokes until the target volume is reached.
In assisted ventilation, the patient himself can determine the times at which he inspires and expires. The ventilation strokes of the apparatus are thus synchronized with the inspiratory and expiratory effort of the patient. The ventilation strokes of the apparatus are volume-controlled or pressure-controlled. In assisted, pressure-controlled ventilation, the ventilator switches between an inspiratory and an expiratory pressure level synchronously with the respiratory effort of the patient.
Assisted ventilation in so-called S mode allows free switching between inspiratory and expiratory pressure (IPAP, EPAP), depending on the breaths initiated by the patient (triggered by spontaneous respiration).
In assisted ventilation in so-called ST mode, the ST mode describes a mixed form of support of spontaneous respiration (S mode) and mandatory ventilation. A background respiratory rate is determined, by which the minimum gap between respiratory intervals is defined. It is possible for the patient to trigger an inspiration within these intervals (from an expiratory phase), i.e., to switch into IPAP by respiratory effort. If the patient fails to trigger an inspiration before the maximum allowed gap is reached, as defined by the background respiratory rate, the ventilator triggers the switch to the inspiratory pressure level to provoke a breath of the patient. This mode also allows mandatory respiration, during which the patient can demand additional breaths.
In another ventilation method, the patient triggers the switch to inspiratory pressure by his respiratory effort. However, he no longer has any freedom with respect to expiration. After a determined inspiratory time, an automatic switch to the expiratory pressure level occurs.